Electrical switches

ABSTRACT

An electrical switch comprises first and second hollow body parts, a conductive plunger mounted in the first body part for axial movement relative thereto and a contact member carried by the second body part. The contact member is engageable by the plunger during axial movement of the plunger from an inoperative position to an operative position and resilient means act on the plunger to urge the plunger to the inoperative position. The first and second body parts are formed with mating screw-threaded portions respectively and one of the body parts has a portion which engages the other body part in a manner to prevent rotation of the one body part relative to the other body part. In a method of assembling an electrical switch of the kind described, the plunger is moved axially relative to the one body part by a distance equivalent to the distance moved by the plunger when the plunger is moved from the inoperative to the operative position, the screw-threaded portions of the body parts are engaged, and the second body part is screwed onto the first body part until indicating means acting between the plunger and the contact member indicate that the plunger is in contact with the contact member, and the screw-threaded portion of at least one of the body parts is deformed so as to secure the body parts in position and prevent relative rotation between the body parts.

United States Patent Gleeson [4 1 Dec.l9, 1972 154] ELECTRICAL SWITCHES [72] inventor: Robert Leonard Gleeson, Burnley,

England [73] Assignee: Joseph Lucas (Industries) Limited,

Birmingham, England 221 Filed: March 15, 1971 21 Appl. No.: 124,180

[30] Foreign Application Priority Data March 20, 1970 Great Britain ..13,695/70 [52] US. Cl ..29/622, 29/407 [51] Int. Cl...I-I0lh 11/00, H0lh 11/02, H0111 11/04, HOlh 65/00 [58] Field of Search.29/622, 407, 203 B, 240, 630 C; 200/83 V, 51.09, 50 B, 166 M [56] References Cited UNITED STATES PATENTS 3,255,521 6/1966 Callahan ..29/407 3,281,664 10/1966 Campbell et al. ..324/28 Primary Examiner-John F. Campbell Assistant Examiner-D. M. Heist Attorneyl-lolman & Stern [5 7] ABSTRACT Anelectrical switch comprises first and second hollow body parts, a conductive plunger mounted in the first body part for axial movement relative thereto and a' contact member carried by the second body. part. The contact member is enga'geable by the plunger during axial movement of the plunger from an inoperative position to an operative position and resilient means act on the plunger to urge the plunger to the inoperative position. The first and second body parts are formed with mating screw-threaded portions respec- .tively and one of the body parts has a portion which engages the other body part in a manner to prevent rotation of the one body part relative to the other body part.

In a method of assembling an electrical switch of the kind described, the plunger is moved axially relative to the one body part by a distance equivalent to the distance moved by the plunger when the plunger is moved from the inoperative to the operative position,

the screw-threaded portions of the body parts are engaged, and the second body part is screwed onto the first body part until indicating me'ans acting between the plunger and the contact member indicate that the plunger is in contact with the contact member, and the screw-threaded portion of at least one of the body parts is deformed so as to secure the body parts in position andprevent relative rotation between the body parts.

4 Claims, 1 Drawing Figure PATENTED 1 9 I97? 3. 706, 133

I NVE NTOQ RQb i w ATTORNEYS ELECTRICAL SWITCHES This invention relates to electrical switches.

An electrical switch, according to the invention comprises first and second hollow body parts, a conductive plunger mounted in said first body part for axial movement relative thereto, a contact member carried by said second body part and engageable by said plunger during axial movement of the plunger from an inoperative position to an operative position, and, resilient means acting on said plunger and urging said plunger to said inoperative position, said first and second body parts being formed with mating screw-threaded portions respectively and one of the body parts having a portion which engages the other body part in a manner to prevent rotation of said one body part relative to said other body part.

The invention further resides in a method of assem bling an electrical switch as described in the preceding paragraph, comprising the steps of moving the plunger axially relative to said one body part by a distance equivalent to the distance moved by the plunger in use when said plunger is moved from said inoperative position to said operative position, engaging .the screwthreaded portion of said second body part with the screw-threaded portion of said first body part, providing indicating means acting between said plunger and said contact member to indicate when said plunger is in contact with said contact member, screwing said second body part onto said first body part until said plunger is in contact with said contact member and then deforming the screw-threaded portion of at least one of the body parts in a manner to secure said body parts in position and to prevent relative rotation between the body parts.

Preferably, the screw-threadedportion of said first body part is formed with an axially extending grove and the screw-threaded portion of the second body part is deformed so that material from said second body part keys into the groove to prevent relative rotation between the body parts.

Preferably, said indicating means is a warning lamp said plunger and said contact member.

The accompanying drawing is a part sectional view of an electrical switch according to one example of the invention.

Referring to the drawing, the switch includes a first hollow,metal body part 11 and a second hollow, synthetic resin body part 12, the first body part 11 being formed with an externally screw-threaded portion 13 which in the'assembled switch mates with an internally screw-threaded portion 14 of the body part 12. A cylindrical conductive plunger 15 is mounted in the body part 11 for axial movement relative thereto, the plunger 15 at one end 150 passing through an annular washer 16 supported by the body part 11 and at its other end projecting from the body part 11. The plunger 15 is provided intennediate its ends with an annular ring 17, a helical compression spring 18 acting between the washer l6 and the ring 17 to urge the plunger to an inoperative position wherein the ring 17 abuts against a shoulder 19 defined within the body part 1 l.

The screw-threaded portion 14 of the second body part 12 is formed with an axially extending groove (not shown) and a hollow, cylindrical contact member 21 is carried by the second body part 12, the contact member 21 at its end remote from the body part 11 defining a terminal of the switch. The other terminal of the switch is defined by the metal body part 11 which will normally be connected to earth and further in the assembled switch the plunger 15 in its inoperative position is coaxial with but spaced from the contact member 21. Thus on movement of the plunger 15 axially into the body part 11 the end 15a of the plunger engages the contact member 21 to complete an electrical circuit through the switch and to define an operative position of the plunger, the washer 16 acting to guide the plunger 15 towards the member 21.

In one practical embodiment (not shown), the switch is used in the braking system of a road vehicle, wherein the braking system includes two identical hydraulic circuits. The braking system further includes a conduit which communicates with said pair of hydraulic circuits and a shuttle movable in said conduit. The shuttle carries a longitudinally extending cam track which is engaged by the outer end of the plunger 15 of the switch in use. The position of the shuttle in the conduit is dependent upon variations in pressure between the two circuits. When both hydraulic circuits are operating normally the shuttle is in a central position in the conduit and the plunger 15 is engaged in a depression in the cam track and is in its inoperative position. However, if one of the hydraulic circuits should fail then the pressure of brake fluid in that circuit will decrease, while the pressure of fluid in the other circuit will remain steady. Thus the shuttle will be moved axially in said conduit away from its central position thereby moving the cam track relative to the plunger 15. The cam track is such that movement of the shuttle depresses the plunger 15 through sufficient distance to engage the contact member 21 and thereby complete an electrical circuit through the switch, for example, to a warning lamp. In this way warning can be given to the driver of the vehicle that one of the hydraulic circuits has failed. I

It will be appreciated that since small fluctuations in the balance of pressure between the two circuits may occur even if both circuits are functioning, then the distance through which the plunger 15 is moved to close the switch must be accurately set if unwanted operation of the switch is to be avoided.

Thus to assemble the switch, the body part 11 is clamped in a jig with the plunger'lS pressed into the body part 11 against the action of the spring 18, so that the end 1500f the plunger is in the same position relative to the washer 16 as that required in the assembled switch when the plunger is in its operative position. The screw-threaded portion 14 of the body part 12 is then engaged with the screw-threaded portion 13 of the body part 11 and the contact member 21 and the plunger 15 are connected in a series circuit (not shown) including a d.c. source and a warning lamp. The body part 12 is then screwed on to the body part 11 until said warning lamp lights up to indicate that the contact member 21 has moved into contact with the end 15a of the plunger 15, the portion 14 of the body part 12 then being hot pressed onto the groove in the portion 13 of the body part 11. Material from the portion 14 is forced into the groove in the portion 13 and provides a key to prevent relative rotation between the body parts in the assembled switch. The assembled switch is then removed from the jig whereafter the spring 18 urges the plunger 13 back to its inoperative position.

I claim:

1. A method of assembling an electrical switch of the kind including first and second hollow body parts, mating screw-threaded portions on the body parts respectively, a conductive plunger mounted in said first body part for axial movement relative thereto, a contact member carried by the second body part and engageable by said plunger during axial movement of the plunger from an inoperative position to an operative position, and resilient means acting on said plunger and urging said plunger to said inoperative position, the method including steps of: a

a. moving the plunger axially relative to the first body part by a distance equivalent to the distance moved by the plunger in use when the plunger is moved from said inoperative position to said operative position,

b. engaging the screw-threaded portion of said second body part with the screw-threaded portion of the first body part,

c. providing indicating means acting between said plunger and said contact member to indicate when said plunger is in contact with said contact member,

d. screwing the body parts into engagement, so as to impart relative axial movement tothe plunger and the contact member, until indication is given by said indicating means that said plunger is in contact with said contact member, and then e. deforming the screw-threaded portion of at least one of the body parts in a manner to secure said body parts in position and to prevent relative rotation between the body parts.

2. A method as claimed in claim 1 wherein the screw.- threaded portion of the first body part is formed with an axially extending groove and the screw-threaded portion of the second body part is deformed so that material from the second body part keys into the groove to prevent the relative rotation between the body parts.

3. A method as claimed in claim 1 wherein the first body part is metal and the second body part is synthetic resin, the deforming operation being carried out by hot pressing the screw-threaded portion of the second body part onto the screw-threaded portion of the first body part.

4. A method as claimed in claim 1 wherein said indicating means is a warning lamp connected in a series circuit including a dc. source, said plunger and said contact member.

a: a a: n: :0: 

1. A method of assembling an electrical switch of the kind including first and second hollow body parts, mating screwthreaded portions on the body parts respectively, a conductive plunger mounted in said first body part for axial movement relative thereto, a contact member carried by the second body part and engageable by said plunger during axial movement of the plunger from an inoperative position to an operative position, and resilient means acting on said plunger and urging said plunger to said inoperative position, the method including steps of: a. moving the plunger axially relative to the first body part by a distance equivalent to the distance moved by the plunger in use when the plunger is moved from said inoperative position to said operative position, b. engaging the screw-threaded portion of said second body part with the screw-threaded portion of the first body part, c. providing indicating means acting between said plunger and said contact member to indicate when said plunger is in contact with said contact member, d. screwing the body parts into engagement, so as to impart relative axial movement to the plunger and the contact member, until indication is given by said indicating means that said plunger is in contact with said contact member, and then e. deforming the screw-threaded portion of at least one of the body parts in a manner to secure said body parts in position and to prevent relative rotation between the body parts.
 2. A method as claimed in claim 1 wherein the screw-threaded portion of the first body part is formed with an axially extending groove and the screw-threaded portion of the second body part is deformed so that material from the second body part keys into the groove to prevent the relative rotation between the body parts.
 3. A method as claimed in claim 1 wherein the first body part is metal and the second body part is synthetic resin, the deforming operation being carried out by hot pressing the screw-threaded portion of the second body part onto the screw-threaded portion of the first body part.
 4. A method as claimed in claim 1 wherein said indicating means is a warning lamp connected in a series circuit including a d.c. source, said plunger and said contact member. 